The present invention relates generally to a bicycle component part, and more particularly to a bicycle front speed changing device.
The bicycle front speed changing device uses a pull cord to draw a link rod mechanism to drive a chain guiding device which guides a chain to swivel aside horizontally, thereby resulting in a change in speed. The pivoting end of the link rod mechanism is divided into an upper swiveling type and a lower swiveling type, which are corresponding in location to the fastening end of the front speed changing device. The drawing of the pull cord is attained by two forms. In the first place, one end of the pull cord runs through the frame bottom and then runs upwards to be fastened with a start end of the link rod mechanism. The start end is pulled by the pull cord to swivel downwards to drive indirectly the chain to displace outwards and horizontally. The second form involves the pull cord which is directly put through a lug of the upright tube to be fastened with the start end of the link rod mechanism. The pull rod does not run through the frame bottom. The start end is pulled to swivel upwards to cause the chain to displace outwards and horizontally.
The second form is not suitable for the front speed changing device of the lower swiveling type. As shown in FIG. 1, one end of the pull cord 1 is put through a lug 2a of the bicycle upright tube 2 to be fastened with a start end 3a of the link rod mechanism 3. The start end 3a must be disposed toward the outer side of the upright tube 2, so as to enable the link rod mechanism 3 to swivel. The pull cord 1 is slanted such that the exposed portion of the pull cord 1 is apt to interfere with the bicyclist""s pants or shoe strings. The front speed changing device of the lower swiveling type is apparently not suitable for use in conjunction with the bicycle having the lug. However, the bicycle upright tube is generally provided with the lug.
The primary objective of the present invention is to provide a front speed changing device which enables the pulling form of the pull cord of the front speed changing device of the lower swiveling type to be widely adaptable.
The front speed changing device of the present invention comprises a base secured to the bicycle frame; a chain guiding member for guiding a chain to displace between a first position and a second position; a first link rod which is pivoted at the first end with the base and is connected at the second end with the chain guiding member; a recovery member for use in enabling the chain guiding member to guide the chain to swivel toward the first position; and a pull cord capable of resisting the recovery force of the recovery member at the time when the pull cord is drawn, thereby causing the chain guiding member to guide the chain to displace horizontally toward the second position. The present invention is characterized by the second link rod which further has an extension end. The first end of the second link rod is located between the extension end and the second end. A driven member is pivoted with the base and has a protruded portion and a start end. A linking member has a first end which is pivoted with the extension end of the second link rod, and a second end which is pivoted with the protruded portion of the driven member. The pull cord is fastened at one end with the start end of the driven member.